1. Field of the Invention
The present invention relates to resin coating compositions for use as coatings for polyolefin-type resins. The resin compositions of the present invention are useful as primer coatings for polyolefin resins. They are also useful as one coat finishing coatings for, casts and films formed of polyolefin-type resins. The coating compositions produce coatings having good adhesive properties, solvent resistance properties and excellent appearance.
2. Description of the Prior Art
The use of polyolefin resins is widespread in the manufacturing industry, for instance in the manufacture of motor vehicles and electric appliances. Such widespread use is due to certain desirable properties possessed by polyolefin resins; for instance they are waterproof, heat proof, resistant to chemicals and electrically insulating. Furthermore, such resins are relatively cheap to produce. For these reasons, demand for such materials is increasing. However, in spite of the merits of the polyolefin resins described above, such resins are crystalline and the formation of strongly adherent coatings on articles formed from such resins are difficult to achieve. It has previously been proposed to enhance the adhesive properties of coated film by subjecting the surface of the polyolefin resin to an acid treatment or to a physical treatment such as corona discharge. Unfortunately, surface treatment by the above physical method is complicated and is costly.
With reference to the improved method of the above process in the case of the surface coating, for example, the coating of the automobile bumpers, many primer compositions have been suggested in order to avoid the need for surface treatments (for instance, see published unexamined patent application No. 95372, 1987 and published unexamined patent application No. 95369, 1987 in Japan). However, the polyolefin-type compositions suggested therein are not sufficiently adhesive to the polyolefin-type resins. Furthermore, according to this prior proposal, a top coat must be provided over the primer coating on the base material which makes the process more complicated. As the coating compositions used for one coat finishing are suggested blends of chlorinated polyolefins and the copolymerized compositions (published unexamined patent application No. 18434, 1987 in Japan).
Unfortunately, however, such blends have inferior weather resistance, humidity resistance and solvent resistance properties and poor film hardness. In order to improve these defects, it has been suggested that a blend of a polymer of an acrylic type or polyurethane type resin with the chlorinated polyolefin could be used (published unexamined patent application No. 15227, 1989 and No. 85226, 1989 in Japan).